Electrode for lead-acid battery

ABSTRACT

The present invention relates to a lead-acid battery Comprising a positive and a negative electrode, each having a current collector comprising an expanded grid, characterized in that at least one of the positive electrode and the negative electrode contains an organic binder in an active material layer at an edge portion thereof. 
     This makes it possible to suppress an internal short circuit resulting from the separation or abnormal growth of an active material due to repeated charge/discharge, thereby remarkably prolonging the cycle life of a lead-acid battery.

TECHNICAL FIELD

The present invention relates to a lead-acid battery comprising anelectrode using an expanded grid as a current collector. The presentinvention further relates to suppressing an internal short circuitresulting from the separation or abnormal growth of an active material,thereby prolonging the cycle life of a lead-acid battery.

BACKGROUND ART

In order to obtain a higher capacity lead-acid battery and to facilitatethe production process of the lead-acid battery, an expanded grid ismostly used these days because an expanded grid can be made thinner thana conventional grid obtained by casting and it can be serially produced.

In a lead-acid battery, the volume change of the active material duringcharging/discharging is relatively large. Accordingly, the repetition ofcharging and discharging weakens the binding force within the activematerial, making it easier for the active material to separate from theelectrode.

In the case where the current collector is a casting grid, it is easy toform a rigid frame around the electrode. The volume change of the activematerial can be suppressed to a certain degree by filling the inside ofthe frame with an active material; accordingly, the separation of theactive material can be prevented.

In the case where the current collector is an expanded grid, on theother hand, unlike the case of a casting grid, it is difficult to form aframe around the electrode because of its production method. Therefore,the active material filling the grid at the right and left edge portionsof the electrode is not surrounded by a frame. As shown in FIGS. 1 and 2which will be used in examples described hereinafter, in a negativeelectrode 5 comprising an expanded grid 1 and an active material layer2, the active material layer 2 is exposed outside at the right and leftportions of the electrode. Thus, the active material at these portionsof the electrode is likely to separate from the electrode due to thevolume change of the active material during charging/discharging. Theseparated active material deposits on the lower portion of theelectrode, which is a cause of short circuit between the positive andnegative electrodes. This internal short circuit degrades the batterycharacteristics.

In a valve regulated lead-acid battery, there are cases where the activematerial grows abnormally at the right and left edge portions of thenegative electrode during the repetition of charging and discharging.The problem arises that the active material grows and reaches thepositive electrode, causing an internal short circuit.

A valve regulated lead-acid battery has a system of reducing an oxygengas generated at the positive electrode into water at the negativeelectrode during charging, which prevents the electrolyte from goingaway outside the system. This system is a cause of the abnormal growthof the active material.

First, oxygen gas generated at the positive electrode reaches thesurface of the negative electrode and is reduced to water by metalliclead of the negative electrode. Meanwhile, the metallic lead of thenegative electrode which has reduced the oxygen gas is oxidized to alead oxide. Subsequently, the lead oxide is dissolved in the electrolyteand is reacted with sulfuric acid to give lead sulfate. The lead sulfateis reduced to metallic lead by receiving electrons at the negativeelectrode.

When the oxygen gas is reduced, metallic lead is required to have asolid-gaseous interface because metallic lead causes solid-gaseous phasereaction with the oxygen gas. Further, the produced lead oxide isreduced to lead sulfate and then to metallic lead; thereby, it ispossible to continuously cause the reduction reaction with the oxygengas. Accordingly, it is of importance that the metallic lead also has asolid-liquid interface.

In view of the above, it is considered that the area where the oxygengas is efficiently reduced into water is the right and left edgeportions of the negative electrode having larger three-phase interfaces(solid, liquid, gas). Accordingly, an apparent charge and dischargereaction occurs more at the right and left edge portions of the negativeelectrode than other portions; inevitably, the volume change of theactive material is significant at the edge portions, making it easierfor the active material to separate.

Moreover, since the reduction reaction of the oxygen gas is a reactionthat accompanies dissolution and deposition, the shape of the activematerial changes significantly. Therefore, the abnormal growth ofmetallic lead is likely to occur at the right and left edge portions ofthe negative electrode.

In order to solve the above problems, for example, Japanese Patent No.2742804 proposes a method in which a positive electrode plate is encasedin a bag-shaped or U-shaped mat separator composed mainly of glass fiberand a negative electrode plate is encased in a bag-shaped separator madeof polymer resin.

Further, Japanese Patent No. 3146438 proposes a method to prevent theseparation of an active material and an internal short circuit byfilling the space between positive and negative electrode plates and theperiphery of the electrode plates with powdered silica.

According to the method described in Japanese Patent No. 2742804, aseparated active material can be maintained at a certain position, andan internal short circuit resulting from the separation of an activematerial can be sufficiently prevented. However, in order to ensure themechanical strength of a separator made of polymer resin in the processto form the separator into a bag shape, the separator is required tohave a certain thickness. If such separator made of polymer resin isinterposed between the positive electrode and the negative electrode,the space between the positive electrode and the negative electrode willbe widened. This increases the resistance of electrolyte, which degradesthe output characteristics of the battery. What is worse is that thismethod cannot prevent the separation of the active material itself.Thus, as charging and discharging are repeated, the amount of the activematerial not involved in charging and discharging increases, whichdecreases the battery capacity.

Moreover, according to a method described in Japanese Patent No.3146438, it is difficult to efficiently fill a battery container withpowdered silica, and a significant effect cannot be expected. What isworse is that the permeation of an oxygen gas or the like generatedduring charging is inhibited. Therfore, it is possible that thereduction reaction of an oxygen gas is inhibited, which causes theelectrolyte depletion.

Furthermore, since the above two methods use a large amount of polymerresin or powdered silica which is not involved in charging/discharging,the space equal to the volume of polymer resin or powdered silica iswasteful and the amount of the active material useful forcharging/discharging is reduced.

In order to solve the above problem, it is an object of the presentinvention to suppress an internal short circuit resulting from theseparation or abnormal growth of an active material, thereby providing alead-acid battery with longer life.

DISCLOSURE OF INVENTION

The present invention relates to a lead-acid battery comprising apositive electrode and a negative electrode, each having a currentcollector comprising an expanded grid, characterized in that at leastone of the positive electrode and the negative electrode contains anorganic binder in an active material layer at an edge portion thereof.

The organic binder preferably has resistance to acids.

The organic binder preferably has resistance to acids and the ability toform a film.

The organic binder preferably comprises a resin containing butyl rubber.

The butyl rubber preferably contains butyl isocyanate.

The organic binder preferably comprises butyl rubber and styrene rubber.

The present invention further relates to a lead-acid battery comprisinga positive electrode and a negative electrode, each having a currentcollector comprising an expanded grid, characterized in that at leastone of the positive electrode and the negative electrode has a porousresin layer formed on the surface of an active material layer at an edgeportion thereof.

The porous resin layer preferably comprises butyl rubber.

The butyl rubber preferably contains butyl isocyanate.

The porous resin layer preferably comprises butyl rubber and styrenerubber.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a (conventional) negative electrodebefore impregnation of an organic binder.

FIG. 2 is an enlarged perspective view of the portion “X” shown in FIG.1.

FIG. 3 is a perspective view of a negative electrode with an organicbinder impregnated therein.

FIG. 4 is a transverse sectional view of a relevant part of a lead-acidbattery of Example 1 of the present invention.

FIG. 5 is a graph showing the relation between the discharge capacityand the cycle number of lead-acid batteries of Examples 1 and 2 of thepresent invention and Comparative Examples 1 and 2.

FIG. 6 is a transverse sectional view of a relevant part of a lead-acidbattery of Example 3 of the present invention.

FIG. 7 is a graph showing the relation between the discharge capacityand the cycle number of lead-acid batteries of Examples 3 and 4 of thepresent invention and Comparative Examples 1 and 2.

FIG. 8 is a graph showing the relation between the discharge current andthe discharge capacity of lead-acid batteries of Examples 3 and 4 of thepresent invention and Comparative Examples 1 and 2.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is a lead-acid battery comprising a positiveelectrode and a negative electrode, each having a current collectorcomprising an expanded grid, characterized in that at least one of thepositive electrode and the negative electrode contains an organic binderin an active material layer at an edge portion thereof.

Herein, FIG. 1 is a perspective view of a conventional negativeelectrode. As shown in FIG. 1, the conventional negative electrodecomprises an expanded grid 1 with a lug portion 1 a and an activematerial layer 2 filling the expanded grid 1. On each side face of thenegative electrode is attached a sheet of paste paper 3. FIG. 2 is anenlarged view of the portion “X” shown in FIG. 1. The conventionalnegative electrode has the problem that an active material couldseparate from the edge portion 4 thereof because the expanded grid 1 isnot surrounded by a frame and the active material layer 2 is exposed atthe edge portion 4, as is apparent from FIGS. 1 and 2.

Accordingly, the present invention is characterized in that the edgeportion 4 of the active material layer 2, which is exposed because ofthe absence of a frame at the edge of the expanded grid 1, contains anorganic binder, as shown in FIG. 3.

It should be noted that the organic binder in accordance with thepresent invention is a material with binding property comprising atleast one organic compound, or a binder comprising at least one organiccompound.

The separation of the active material can be prevented since the organicbinder contained in the active material layer at the edge portion of theelectrode maintains its binding force within the active material whosevolume changes during charging/discharging. It is preferred that thelower edge portion also contains the organic binder in order to insulatethe electrode from separated active material.

Additionally, the above-described effect can be achieved if at least,the periphery of the surface of the active material layer at the edgeportion of the electrode contains the organic binder. It is morepreferred that the whole active material layer contains the organicbinder because that can further strengthen the binding force within theactive material.

It is also preferred that the organic binder has resistance to acids.When the organic binder is used in a lead-acid battery, stable bindingforce can be maintained for a long period of time.

It is further preferred that the organic binder has the ability to forma film. Covering the active material with a much less reactive filmsuppresses the charging/discharging reaction at the covered portion.This reduces the volume change of the active material resulting from thecharging/discharging reaction, making it easy to maintain the bindingforce within the active material.

The organic binder film may be formed not only on the surface of theactive material at the edge portion of the electrode, but also on theexpanded grid itself. In such a case, the effect of insulating theelectrode from separated active material enhances.

It is preferred that the above-mentioned organic binder comprises aresin containing butyl rubber. Since butyl rubber is tough and flexible,it is easy to maintain the binding force even if the volume of theactive material changes.

The components of butyl rubber include isobutylene and butyl isocyanate,etc. They may be used singly or in combination. Among them, butylisocyanate is more preferred. Butyl isocyanate forms a three-dimensionalcrosslinked structure by a urea bonding and a biuret bonding; thereby, atough and flexible resin can be formed.

It is also possible to further increase flexibility and toughness bymixing butyl rubber and styrene rubber.

Although toluene is typically used as the solvent dissolving the mixtureof butyl rubber and styrene rubber, the use of xylene or other solventcapable of dissolving the aforesaid organic binder components gives asimilar result. The use of their mixture also gives a similar result.

Further, the present invention is related to a lead-acid batterycomprising a positive electrode and a negative electrode, each having acurrent collector comprising an expanded grid, characterized in that atleast one of the positive electrode and the negative electrode has aporous resin layer formed on the surface of an active material layer atan edge portion thereof. There is no need to mention that the porousresin layer may cover the edge of the expanded grid.

The porous resin layer maintains the binding force within the activematerial of the electrode at the edge portion thereof; thereby, theseparation of the active material can be prevented and the internalshort circuit which occurs due to separated active material can beprevented. Herein, the porous resin layer is a porous body with throughholes. Thus, it enables the permeation of oxygen gas generated duringcharging without impeding the diffusion of electrolyte; furthermore, thediffusion of oxygen gas is not impeded.

A similar effect can be obtained even when the porous resin layer havingthrough holes covers not only the surface of the active material layerbut also the periphery of the surface of the active material layer.

It is preferred that the porous resin layer comprises butyl rubber.Since butyl rubber is superior in resistance to acids, the initialperformance can be maintained for a long period of time.

It is preferred that the butyl rubber contains butyl isocyanate. Sincebutyl isocyanate forms a three-dimentional crosslinked structure when itis cured, the active material can be securely retained. Further, sincebutyl isocyanate is superior in resistance to acids, the effect can lastfor a long time.

It is preferred that the porous resin layer comprises the mixture ofbutyl rubber and styrene rubber. Because the use of the mixtureincreases the flexibility compared to the case of using butyl rubberonly, it is possible to respond more flexibly to the volume change ofthe active material.

The porous layer in the porous resin layer can be formed by using afoaming agent.

In the case where a thermal decomposition type foaming agent is added tobutyl rubber, for example, part of the component obtained bydecomposition during heating of a thermal decomposition type foamingagent supports the three-dimensional crosslinked structure of the butylrubber. The remaining of the decomposed component includes a gas and apolymeric residue. Foam is formed within the resin layer by the gascomponent, and the foam is connected to form through holes. Afterthrough holes are formed, the gas generated is removed with the solvent.Accordingly, the gas hardly remains in the porous resin layer as animpurity.

On the other hand, although the polymeric residue remains in the resinlayer, there is a method to effectively employ it. For example, whenhydrophilicity is imparted to the porous resin layer, a foaming agentfor allowing sulfone group to remain as a residual substituent should beselected.

Preferred thermal decomposition type foaming agent includeazodicarbonamide, dinitrosopenta-methylene-tetramine, 4,4′-oxybisbenzene sulfonyl hydrazide, etc. There are many other foaming agentswhich have different foaming temperature and different decomposedproducts because of the differences in structure, molecular weight,substituent, etc. Accordingly, it is possible to adjust the porosity,diameter, thickness and size of resin skeleton of the porous resinlayer. They can be used optionally according to the purpose, or they canbe used in combination of two or more.

The porosity of the porous resin layer can be set freely by selectingthe type of foaming agent, controlling the added amount, etc.Preferably, the porous resin layer has a porosity of 30 to 90%. When theporosity exceeds 90%, the diffusion of the electrolyte or the permeationof the oxygen gas during charging/discharging is not be inhibited, butthere is a possibility that an internal short circuit occurs because theactive material reaches the counter electrode via through holes.

Conversely, when the porosity is less than 30%, the number of throughholes is reduced, inhibiting the diffusion of the electrolyte or thepermeation of the oxygen gas.

In the following, examples of the present invention are explained indetail. It is to be understood that the present invention is not limitedto the examples. Although the examples of the present invention usevalve regulated lead-acid batteries, it has been confirmed that the useof a flooded lead-acid battery also gives a good result.

EXAMPLE 1

(i) Production of Negative Electrode

Slits were made in a lead-tin-calcium alloy sheet consisting of 0.08 wt% of calcium, 0.8 wt % of tin and the rest amount of lead, which wasthen expanded to form squares. Thereby, an expanded grid 1 with a lugportion 1 a was produced.

A negative electrode paste was prepared by mixing powdered lead, water,sulfuric acid with a specific gravity of 1.41, powdered carbon (DENKABLACK), barium sulfate, a lignin derivative and polyester staple fiberat a weight ratio of 1000:115:70:4.1:21:4.1:1, followed by kneading.

The above-obtained expanded grid 1 was filled with the negativeelectrode paste to form an active material layer 2. Then, a sheet ofpaste paper 3 made of kraft pulp and reinforcement for preventing theseparation of the active material was attached to each side face of theelectrode, which was then cured and dried to give a negative electrode 5as shown in FIGS. 1 and 2.

(ii) Addition of Organic Binder to Active Material Layer at the Rightand Left Edge Portions of Negative Electrode

Butyl rubber and styrene rubber were mixed at a weight ratio of 97:3. Aresin solution was prepared by dissolving 30 parts by weight of theobtained mixed resin in 70 parts by weight of toluene. The right andleft edge portions 4 of the negative electrode 5 were respectivelyimmersed in the resin solution. After the active material layer 2 at theedge portion 4 of the negative electrode 5 was impregnated with theresin solution, it was dried at 120° C. to remove toluene. Duringdrying, the organic binder comprising butyl rubber and styrene rubberpermeated through the active material layer 2 at the right and left edgeportions of the negative electrode 5, and the surface of the activematerial layer 2 was covered with a film of the organic binder. FIG. 3shows the negative electrode after impregnation of the organic binder.

(iii) Production of Positive Electrode

Slits were made in a lead-tin-calcium alloy sheet consisting of 0.08 wt% of calcium, 1.2 wt % of tin and the rest amount of lead, which wasthen expanded to form squares. Thereby, an expanded grid was produced.

A positive electrode paste was prepared by mixing powdered lead, water,sulfuric acid with a specific gravity of 1.41, tin sulfate (SnSO₄) andpolyester staple fiber with a length of 2 mm and a diameter of 10 μm ata weight ratio of 1000:115:70:10:1, followed by kneading.

The above-obtained expanded grid 6 was filled with the positiveelectrode paste. Then, a sheet of paste paper made of kraft pulp andreinforcement for preventing the separation of the active material wasattached to each side face of the electrode, which was then cured anddried to give a positive electrode 8.

(iv) Assembly of Lead-Acid Battery

There were prepared twelve positive electrodes 8 obtained in the above,thirteen organic binder imparted negative electrodes 5 and twelve glassmat separators 9 obtained by forming glass fiber with a diameter of 3 to5 μm and one with a diameter of 0.5 to 1.0 μm into a sheet. Theaforesaid separator 9 was folded in half and the positive electrode 8was encased in the folded separator, which was then stacked alternatelywith the negative electrode. FIG. 4 shows a sectional view of a part ofthe stack. A strap for collecting currents was formed on the stack bycasting to give an electrode assembly. This electrode assembly wasinserted into a battery container, and the strap was resistance-weldedto connect cells. Then, a battery container lid was provided. Dilutesulfuric acid electrolyte solution with a specific gravity of 1.30containing 10 g/L of sodium sulfate was poured into the batterycontainer, and a safety valve was provided to obtain a sealed lead-acidbattery with a rated voltage of 12 V and a nominal capacity of 65 Ah.This battery was referred to as Battery A.

EXAMPLE 2

A sealed lead-acid battery with a rated voltage of 12 V and a nominalcapacity of 65 Ah was produced in the same manner as in Example 1,except that the organic binder was impregnated in the active materiallayer at the right and left edge portions of the positive electrodeusing the same method as in Example 1, instead of the negativeelectrode. The battery was referred to as Battery B.

COMPARATIVE EXAMPLE 1

A sealed lead-acid battery with a rated voltage of 12 V and a nominalcapacity of 65 Ah was produced in the same manner as in Example 1,except that the negative electrode did not have the organic binder inthe active material layer at the right and left edge portions thereof.The battery was referred to as Battery C.

COMPARATIVE EXAMPLE 2

Eleven positive electrodes, which were the same as those in ComparativeExample 1, respectively sandwiched between in a glass mat separators,which were the same as those in Example 1, were produced. Meanwhile,twelve negative electrodes, which were the same as those in ComparativeExample 1, respectively encased in bag-shaped non-woven-fabric made ofsynthetic resin fiber with a thickness of 0.2 mm which was subjected tohydrophilicity treatment were produced. They were alternately stacked togive an electrode assembly. A sealed lead-acid battery with a ratedvoltage of 12 V and a nominal capacity of 60 Ah was produced in the samemanner as in Example 1 using the electrode assembly. The battery wasreferred to as Battery D.

[Evaluation of Batteries]

Batteries A to D obtained in the above were put through a 1/3 CAdischarge cycle life test at 25° C. The discharge was performed at aconstant current of 1/3 CA to 80% of discharge depth. The charge wasperformed at a constant current of 0.2 CA until the battery voltagereached 14.4 V, and after that, at a constant current of 0.05 CA for 4hours. The charge and the discharge were performed alternately. Thebatteries were completely discharged at every 20 cycles. Subsequently,their capacities were checked. FIG. 5 shows the evaluation results.

As is apparent from FIG. 5, the capacity of Battery C was remarkablylowered after about 180 cycles and it was below 80% of the initialdischarge capacity after 210 cycles. On the other hand, the capacitiesof Batteries A, B and D were over 90% of the initial discharge capacityeven after 800 cycles (Batteries A, B and D had an initial dischargecapacity of 61.0, 60.0 and 56.0 Ah respectively and a discharge capacityafter 800 cycles of 55.5, 54.0 and 50.6 Ah respectively).

Battery C was disassembled to find that metallic lead deposited on thenegative electrode at the side of the electrode assembly and themetallic lead reached the positive electrode, skirting the glass matseparator. This proved that the cause of the remarkable decrease incapacity of Battery C was an internal short circuit.

Battery A was disassembled in the same manner after 800 cycles. Theedges of the electrode assembly were checked to prove that the growth ofthe active material at the right and left edge portions of the negativeelectrode similar to the case of Battery C was not found. The separationof the active material was found at the right and left edge portions ofthe positive electrode; however, the amount of the active materialseparated was small and the separated active material did not extendfrom the glass mat separator. Presumably, this is because, in the valveregulated lead-acid battery, the stacking pressure of the electrodeassembly was high and the active material was sufficiently pressed byglass mat separators.

Battery B was disassembled in the same manner to find that metallic leadextended from the right and left edge portions of the negativeelectrode, similar to the case of Battery C. However, the organic binderimparted to the right and left edge portions of the positive electrodehad no conductivity and the binder formed a film on the surface of theactive material. Accordingly, there was no electrical contact.Additionally, the separation of the active material was not found at theright and left edge portions of the positive electrode.

EXAMPLE 3

FIG. 6 shows a transverse sectional view of a relevant part of thelead-acid battery of the present example.

After a negative electrode 5 was produced in the same manner as inExample 1, a porous resin layer 10 having through holes was formed onthe surface of an active material layer 2 at the right and left edgeportions 4 of the negative electrode 5 by the following process.

Butyl rubber and styrene rubber were mixed at a weight ratio of 97:3. Aresin solution was prepared by dissolving 30 parts by weight of theobtained mixed resin in 70 parts by weight of toluene. In the resinsolution was dispersed azodicarbonamide as a foaming agent, and theright and left edge portions of the negative electrode 5 wererespectively impregnated with the dispersion. Subsequently, it wasfoamed at 210° C. and, at the same time, toluene as the solvent wasremoved therefrom. During this process, part of the resin componentpermeated the periphery of the surface of the active material layer 2. Aporous resin layer 10 with a thickness of 0.05 mm on the surface wasformed, and the porous resin layer had a porosity of 55%.

Using the above-obtained negative electrode and positive electrode andglass mat separator which were analogous to those in Example 1, a sealedlead-acid battery with a rated voltage of 12 V and a nominal capacity of65 Ah was obtained in the same manner as in Example 1. The battery wasreferred to as Battery E.

EXAMPLE 4

A sealed lead-acid battery with a rated voltage of 12 V and a nominalcapacity of 65 Ah was obtained in the same manner as in Example 3,except that the porous resin layer having through holes was formed onthe surface of the active material at the right and left edge portionsof the positive electrode using the same method as in Example 3, insteadof the negative electrode. The battery was referred to as Battery F.

Batteries E and F were put through the same cycle life evaluation as inExample 1. FIG. 7 shows the evaluation results. It also shows theresults of Batteries C and D for comparison.

FIG. 7 indicated that Batteries E and F respectively maintained acapacity of over 90% of the initial discharge capacity even after 800cycles. (Batteries E and F had an initial discharge capacity of 61.0 and60.0 Ah respectively and a discharge capacity after 800 cycles of 55.0and 54.0 Ah respectively). Batteries E and F were disassembled in thesame manner as in Example 1 after 800 cycles to find that Batteries Eand F were in the same condition as Batteries A and B.

Separately from the cycle evaluation, discharge characteristics at theinitial state were evaluated. FIG. 8 shows the evaluation results.

FIG. 8 indicated that Batteries E and F had similar dischargecharacteristics as Battery C and had higher discharge characteristicsthan Battery D. Presumably, this is because the distance betweenelectrodes of Batteries E and F was smaller by the thickness of thenon-woven fabric made of synthetic resin, which reduced the resistanceof electrolyte during discharging.

INDUSTRIAL APPLICABILITY

As described above, the present invention can provide a lead-acidbattery with longer life by suppressing an internal short circuitresulting from the separation or abnormal growth of an active materialdue to repeated charge/discharge.

Further, the present invention can provide a lead-acid battery withlonger life and good discharge characteristics, without impairing outputcharacteristics, by forming a porous resin layer with through holes onthe surface of an active material layer at the edge portion of anelectrode.

1. A lead-acid battery comprising a positive electrode and a negativeelectrode, each having a current collector comprising an expanded grid,characterized in that at least one of said positive electrode andnegative electrode contains an organic binder in an active materiallayer, said organic binder being contained only at a circumferentialedge portion of said active material layer, wherein the organic bindercomprises at least one of butyl rubber and styrene rubber.
 2. Thelead-acid battery in accordance with claim 1, wherein said butyl rubbercontains butyl isocyanate.
 3. The lead-acid battery in accordance withclaim 1, wherein said expanded grid includes at least one hole extendingfrom a first surface to a second surface, said active material layerbeing included in said at least one hole.
 4. The lead-acid battery inaccordance with claim 1, said active material layer includes first andsecond surfaces on opposite sides of said active material layer and athird surface extending from said first surface to said second surfacein a thickness direction of said active material layer, saidcircumferential edge portion including said third surface and only aportion of said first and second surfaces.
 5. A lead-acid batterycomprising a positive electrode and a negative electrode, each having acurrent collector comprising an expanded grid, characterized in that atleast one of said positive electrode and negative electrode has a porousresin layer formed on a side surface of an active material layer, saidactive material layer includes first and second surfaces on oppositesides of said active material layer and said side surface extends fromsaid first surface to said second surface in a thickness direction ofsaid active material layer, a portion of said porous resin layer formedon said side surface extends from said first surface to said secondsurface, said porous resin layer being formed only at an edge portion ofsaid active material layer, wherein said edge portion includes said sidesurface and only a portion of said first and second surfaces.
 6. Thelead-acid battery in accordance with claim 5, wherein said porous resinlayer comprises butyl rubber.
 7. The lead-acid battery in accordancewith claim 6, wherein said butyl rubber contains butyl isocyanate. 8.The lead-acid battery in accordance with claim 5, wherein said porousresin layer comprises butyl rubber and styrene rubber.
 9. The lead-acidbattery in accordance with claim 5, wherein said expanded grid includesat least one hole extending from the first surface to the secondsurface, said active material layer being included in said at least onehole.